In conventional centrifuges, containers for a sample are carried by a rotor and the rotor is driven in rotation at high speed by an electric motor to produce high centrifugal force. The rotary mechanism including the rotor and the motor is conventionally supported on a stationary casing by at least one coil spring in order to obtain stable high speed rotation without transmission of vibration. The centrifuge with this rotary system has a mechanical natural frequency, that is, a resonance point, and it is conventional, for obtaining stable high speed rotation, to rotate the rotor at a speed which is much higher than the natural frequency. Accordingly, in using the centrifuge, it is unavoidable for the rotor to pass through the natural frequency, that is, the resonance point during running up to speed and during slowdown when stopping. If the rotary body has an unbalanced weight condition, there is caused the danger that at the moment when the rotary body passes through the resonance point, the rotor is substantially vibrated and the sample-containing containers carried by the rotor fly off or the sample placed in the centrifuge is disordered, so that operation of the centrifuge becomes unprofitable. Accordingly, it has been conventional to balance the rotor and the sample containers, and additionally, the amount of the sample to be introduced in the containers is weighed each time when it is put into each container in order to obtain proper balancing. Thus, use of the centrifuge becomes troublesome.